Hypersensitive baboons will be exposed to sulfur dioxide, nitrogen dioxide, and a combination of the two, at realistic levels to assess the effects of such exposure upon (1) spontaneous release of histamine and SRS-A from circulating leukocytes and lung mast cells, (2) possible alterations in subsequent antigen-antibody mediated release of the mediator substances as assessed by both allergen challenge and in vitro reversed anaphylaxis, and (3) changes in membrane-bound enzyme function resulting from the exposure as assessed by alterations in intracellular cyclic AMP levels. The same parameters will be assessed in in vitro exposure experiments utilizing circulating leukocytes and lung tissue obtained at necropsy.